1. 1 Lymphatic System One way system: to the heart Return of collected excess tissue fluid Return of leaked protein “Lymph” is this fluid Edema results if system blocked or surgically removed

2. 2 Lymph capillaries  Have one way minivalves allowing excess fluid to enter but not leave  Picks up bacteria and viruses as well as proteins, electrolytes and fluid (lymph nodes destroy most pathogens)

3. 3

4. 4 Lymph capillaries  Absent from bone, bone marrow, teeth, CNS  Enter lymphatic collecting vessels Lymphatic collecting vessels  Similar to blood vessels (3 layers), but thin & delicate  Superficial ones in skin travel with superficial veins  Deep ones of trunk and digestive viscera travel with deep arteries  Very low pressure  Distinctive appearance on lymphangiography  Drain into lymph nodes

5. 5 Lymph nodes: bean shaped organs along lymphatic collecting vessels Up to 1 inch in size Clusters of both deep and superficial LNs

6. 6 Superficial groups -Cervical -Axillary -Inguinal Deep groups -Tracheobronchial -Aortic -Iliac Drainage -Superior R 1/4 of body: R lymphatic duct (green) * -The rest: thoracic duct * Lymph Nodes * *

7. 7 Fibrous capsule sends in dividing trabeculae Afferent & efferent lymphatic vessels Lymph percolates through lymph sinuses Follicles: masses of lymphoid tissue divided into outer cortex & inner medulla (details in later slides)

8. 8 Macrophages on reticular fibers consume pathogens and foreign particles Usually pathogen free lymph enters lymph trunks

9. 9 Lymphatic Trunks (all are paired except the intestinal trunk) Lumbar Intestinal  Receives fatty lymph (chyle) absorbed through lacteals in fingerlike villi of intestines Broncho- mediastinal Subclavian Jugular

10. 10 Lymph ducts (variable) Thoracic duct: everyone has 20% also have a right lymphatic duct * 20%

11. 11

12. 12 Lymphoid Organs Lymph nodes Spleen Thymus Tonsils Small intestine & appendix aggregated lymphoid nodules

13. 13 Lymphoid Tissue Specialized connective tissue with vast quantities of lymphocytes  Lymphocytes become activated  Memory  Macrophages & dentritic cells also  Clusters of lymphoid nodules or follicles

14. 14 Thymus Prominent in newborns, almost disappears by old age Function: T lymphocyte maturation (immunocompetence) Has no follicles because no B cells

15. 15 Lymph Nodes Lymphatic and immune systems intersect Masses of lymphoid tissue between lymph sinuses (see next slide) Some of antigens leak out of lymph into lymphoid tissue Antigens destroyed and B and T lymphocytes are activated: memory (aiding long-term immunity)

16. 16 Follicles: masses of lymphoid tissue divided into outer cortex & inner medulla All follicles and most B cells: outer cortex Deeper cortex: T cells, especially helper T cells Medullary cords: T & B lymphocytes and plasma cells

17. 17

18. 18 lymphangiogram

19. 19 Spleen Largest lymphoid tissue; is in LUQ posterior to stomach Functions  Removal of blood-borne antigens: “white pulp”  Removal & destruction of aged or defective blood cells: “red pulp”  Stores platelets  In fetus: site of hematopoiesis Susceptible to injury; splenectomy increases risk of bacterial infection

20. 20 Spleen

21. 21 Palatine (usual tonsillitis) Lingual (tongue) Pharyngeal (“adenoids”) Tubal Tonsils * * * Simplest lymphoid tissue: swellings of mucosa, form a circle Crypts get infected in childhood

22. 22

23. 23 Aggregated lymphoid nodules (“Peyer’s Patches”)  About 40 follicles, 1 cm wide  Distal small intestine (ileum) Appendix Parts of the intestine are so densely packed with MALT (mucosa-associated lymphoid tissue) that they are considered lymphoid organs